From my experience vegans tend to have few or no children. This could be due to the fact that many vegans that I know are young, or the fact that - as said in this answer - vegans tend to have a higher education and be professionals, two things that usually correlate with lower number of children.
Do vegans have less children or is my personal perspective that tells me that? Are there any studies on this subject? (perhaps studies that make hypothesis on the reasons too)